Reading Comprehension

PT155 · S3 · P3 · Q18 Nanoscale Computer Chips

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This passage was adapted from an article published in 2000.

Topic

Belcher and Hu's research using peptides — short amino-acid chains — to build nanoscale electronic components.

Framework

Highlight Noteworthy. The author isn't arguing against anyone; the author is showcasing a promising approach to a coming problem in chip miniaturization.

Main Point

Conventional miniaturization is about to hit a hard physical limit, and Belcher and Hu's peptide-based approach is a promising route to building electronics below that limit. They have already identified hundreds of peptides that bind to specific semiconductor crystals and are now designing peptides that can act as molecular "glue" — exactly the kind of finesse needed for self-assembling nanocircuits.

P1: Why this work matters

The race to make computer chips smaller is approaching a wall (~2010): current transistors can't go below 25 nanometers. Living cells, however, routinely build complex structures at smaller scales. So researchers want to harness biological molecules. Most work focuses on DNA — Belcher and Hu are pursuing peptides instead.

P2: How they got there

The idea grew out of Belcher's discovery that a specific peptide directs calcium-carbonate crystallization in abalone shells. She and Hu reasoned that peptides able to direct crystal growth in semiconductor materials could be a tool for building nanoscale electronics. Since no known peptide had this property, they screened a billion random peptides against three semiconductor materials and isolated ones that bound to specific faces of specific crystals — then refined them via accelerated-evolution-style methods.

P3: Where things stand and what's next

To assemble a real toolkit, many more binding peptides are needed. They're making progress: hundreds of crystal-manipulating peptides across 20+ semiconductor materials, plus newly designed peptides that bind to two different crystals at once — molecular glue. That kind of nanoscale finesse is what self-assembling circuits will require.

18.

Which one of the following statements about the peptides that Belcher and Hu tested in relation to semiconductors can be most reasonably inferred from the passage?

  1. Correct

    At least some of them

    Why this is right

    Remember it's "most reasonably inferred". We might not have must-be-true proof of this, but the gist is there: - "no known peptide could do what they want" - "grew a random assortment of one billion of them" - "they developed additional related peptides from the promising ones they had found" Each of those is suggestive of this answer choice. If no known peptide could do what they want, then they sought find something that didn't already exist in nature (technically, something that had not yet been discovered in nature). By growing a random assortment of one billion of them, it seems very likely that they happened to get some random ones that don't exist in nature. And then the active sense of developing, or genetically engineering, the type of peptide they want insinuates that they were now playing God.

    Skill tested: Inference · how this choice captures the passage's function is the move to repeat next time.

    60% picked this

  2. At least one of them

    Out of Scope: bound to three

    It's very plausible that this happened, but there isn't any textual support for it. The paragraph stressed that they found a few peptides that only bind to one of the three compounds, but that doesn't tell us that some of the peptides bound to all three.

    17% picked this

  3. At least some of them

    Too Specific: S but not GA

    Silicon, gallium arsenide, and indium phosphide are all treated interchangeably in the once sentence we hear about them. We don't have any support for the idea that some peptides were tested for S but not for GA.

    9% picked this

  4. At least one of them

    Contradicted

    This seems to go against that line that "no known peptide was able to bind to semiconductor materials". And the fact that they grew a random assortment doesn't sound like they're recycling peptides that are already used in the computer chip industry.

    6% picked this

  5. Other researchers had previously tested

    Out of Scope

    Out of Scope: other than S, GA, IP The line that says "no known peptide was able to bind to semiconductor materials" does seem to suggest that some people had already tried to see if they could find a peptide that binds to semiconductor materials, but we'd have no idea which semiconductor materials were used. Given that S, GA, and IP are three widely used semiconductor materials it would be plausible that previous research also would have tested those materials. Ultimately, we're just speculating either way, which is why the answer is unsupportable.

    8% picked this

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